A network file system called Multifile is described. It meets response, availability, and stability requirements as primitive functions. Multifile has a high degree of responsiveness because its component parts compete among themselves to service file requests; it has high availability because it maintains multiple copies of files; and it exhibits stable behavior over wise range of system parameters. The responsiveness of Multifile to read requests improves as the number of pages per request rises, implying that read ahead pages can profitably be cached at client sites. The throughput of Multifile improves as the request size increases and as the number of clients increases. As server load increases, the responsiveness of Multifile to read requests is stable in most configurations. The throughput of writes is unstable as the number of pages in the wire request rises, implying that write back pages should not be cached at client sites. The scale of events in file service is dominated by disk activity, so lost message exceptions do not occur frequently enough to affect file service; however, duplicate message exceptions are a factor in performance.>

A model paging system is described for write-once optical disk. The paging system checkpoints pages on a nonerasable, failure-resistant medium as a side effect of virtual memory operation. Most pages are already checkpointed at any given time. It is practicable to checkpoint the global state periodically by forcing the write-out of pages that have been modified since their last checkpoint, together with the page tables. The proposed checkpointing algorithm was simulated to evaluate the performance of paging and checkpoint to write-once optical disk. There are plausible values for the operating parameters that make the overhead of checkpointing negligible compared to paging. The lifetime of 1-GB write-once optical disk media used for paging and checkpointing can range up to three months under plausible operating conditions.>

A kernel is described, called the link kernel, for high-performance interprocess communication among shared-memory multiprocessors using an Ethernet. The link kernel provides asynchronous multicast communication service without protocol overhead. Links are created by listeners, and processes may be simultaneously talkers and listeners. Processes access links through a global link table. Multicast addresses are site-independent, so communication is independent of process locations in the network. Communication is asynchronous, so much of the overhead of message management is masked by parallel computation.>

Abstract This paper reports on an experimental study of the probe effect, defined as an alteration in the frequency of run‐time computational errors observed when delays are introduced into concurrent programs. If the concurrent program being studied has no synchronization errors, then there is no probe effect. In the presence of synchronization errors, the frequency of observable output errors for a sample experimental program starts at a high value for small delays, oscillates rapidly as the delay is increased, and apparently settles at zero errors for larger values of delay. Thus, for sufficiently large delays, the probe effect can almost completely mask synchronization errors in concurrent programs. For sufficiently large concurrent process sets, even small values of embedded delay may mask synchronization errors, provided side effects in shared memory are not included in the observation.

Abstract This paper reports on an experimental debugger for concurrent programs. Design objectives include a showing of greatest usefulness when dealing with multiprocess interactions, creation of a simplified more approachable interface for programmers, allowance for the systematic organization (and limitation) of debugging information by programmers, reflection of a natural view of concurrency, and portability. The design responds to a perceived need for debugging techniques applicable in systems of concurrent, communicating, asynchronous processes. During debugging sessions, a user is able to dynamically explore interprocess synchronization points, parallel actions and deadlock situations. The programmer interface is based on a transparent window multiplexer providing a set of windows for each concurrent process. The window manager interactively maps interesting windows to programmer‐specified viewscreen locations, while relegating temporarily uninteresting windows to the background. In implementing a debugger for concurrent programs, a principal concern is the probe effect, or the possibility that the debugger itself masks synchronization errors in the program being debugged. For the examples explored, the probe effect was not observed to limit the localization of implanted synchronization errors.

Aesthetics in user interfaces addresses font definitions, typesetting conventions, color combinations, graphics design considerations, high resolution for viewscreens, and the shapes of windows. Computer viewscreens are evolving into pictorial media, communicating information with visual immediacy. The more interesting interfaces make use of multiple windows, menus, icons, and other visual effects to waken and sustain user interest and effectiveness. A pretty window is a viewscreen window with the dimensions of a golden rectangle, a rectangle whose width and height form the golden ratio of Euclid. Psychologists believe golden rectangles are aesthetically more pleasing than arbitrary rectangles, and subjects tend to select them in preference to other rectangles in tests.

This paper focuses on selected aspects of communications security for electronic funds transfer systems that may not be present in classical security-oriented communications systems. 1) An EFT security system should be able to pinpoint the site responsible for any financial loss resulting from a penetration. 2) An EFT security system should not allow false rejections, i.e., should not deny any legitimate transaction. 3) An EFT security system should not employ draconian methods to restore communications security after a penetration. 4) Simultaneous accesses to an EFT account should be synchronized to ensure that improper transactions are not authorized. 5) Traditional access-control methods applied to secure commumcations equipment are not applicable to EFT networks. 6) Traditional manually oriented techniques used to distribute encryption keys may not be practicable in a large scale EFT network. 7) Techniques used in providing communications security, especially those involving encryption algorithms, should not rely on secrecy to protect the integrity of the system. 8) Communications overhead imposed by security measures should be minimized to allow for projected high rates of use of EFT facilities.

During the next few years a new pseudorandom number generator will become available on many computer systems. A concern for the security of computer data has led to the adoption of a Data Encryption Standard (DES) by the National Bureau of Standards. This standard specifies a nonlinear cryptographic algorithm which can be used inter alia as a source of pseudorandom numbers in software applications, such as those involving order statistics, where the usual linear congruential and generalized feedback shift register generators seem to be inadequate. Results of testing the DES as a pseudorandom number generator indicate that the algorithm is more than satisfactory for this purpose.